Optical data communication systems provide an important way for transferring large amounts of data at high speeds. An important component in these optical data communication systems is an optical transceiver (TRANSmitter+reCEIVER). On the transmission side, the optical transmitter portion functions to translate data in the form of electrical signals (e.g., digital information in the form of 1s and 0s) into optical signals that are suitable for transmission via a transmission medium (e.g., fiber optic cable). On the reception side, the optical receiver portion converts the received optical signals back into data in the form of electrical signals. An important component in the optical transceiver design is the transmitter for transmitting optical data. Typically, the transmitter is implemented with a light emitting diode (LED) for megabit applications and a semiconductor laser diode for gigabit applications.
Semiconductor laser diodes were originally fabricated in a manner that provides an optical cavity formed parallel to the surface of the semiconductor wafer. In this structure, light is emitted from the edge of the wafer. Unfortunately, this structure does not lend itself to low cost “mass” manufacturing or to the cost-effective fabrication of two-dimensional arrays of laser diodes.
A new class of laser diodes is fabricated such that the optical cavity is formed perpendicular to the surface of the semiconductor wafer, and the light is emitted perpendicular to the surface. These laser diodes are commonly referred to as Vertical Cavity Surface-Emitting Lasers (VCSELs). A typical VCSEL consists of an active region, which emits light and surrounding mirrors constructed from alternating layers of materials having different indices of refraction. These lasers are better suited for the fabrication of arrays and are widely utilized in optical data communication systems.
Vertical Cavity Surface Emitting Lasers (VCSELs) are considered to be important components in optical communication systems. VCSELs can easily be made into one and two-dimensional arrays since they emit light perpendicular to the plane of the semiconductor wafer.
High Speed Design Considerations
As the demand for bandwidth in optical communication systems ever increases, new design considerations and mechanisms are required to achieve these types of data transmission speeds. Currently, there are two main approaches to increase bandwidth. One approach utilizes directly modulated lasers. However, this first approach is generally limited to data rates of about 10 Gb/s.
A second approach utilizes external modulators. This second approach can generally achieve data rates of up to about 40 Gb/s, which is greater than the first approach. However, the use of external modulators adds additional complexity to the transmitter design and is typically expensive to implement. Furthermore, many external modulators require high voltages for modulation, thereby further increasing the cost and complexity of the transmitter design.
Unfortunately, the prior art approaches do not provide any mechanism to increase the data rate of current VCSELs without the use of external modulators. Consequently, it is desirable for there to be a VCSEL design that extends the current data rates beyond current limitations without the use of external modulators.
Based on the foregoing, there remains a need for a vertical cavity surface emitting laser (VCSEL) that overcomes the disadvantages set forth previously.